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Simply Cracking!

On early cracking in concrete – how it happens, why it is such a concern, and how it can be prevented.

Simply Cracking!
06 March 2018 Posted in ,

Early cracking in concrete is so commonplace as to be hardly worth discussion – right? Who hasn’t seen a new floor slab, for instance, already crazed with hairline cracks? Fact is, these fine cracks are not insignificant. They are a serious weak point in the innate strength of the concrete.

CAUSE

For a brand new slab, there are two main causes of surface cracking.

1. PLASTIC SETTLEMENT CRACKING

— There is no plastic in Plastic Settlement Cracking … except maybe the reo bar stools. The term ‘plastic’ refers to the malleable condition of the concrete. When we talk about Plastic Cracking in the context of concrete, we mean cracking that occurs while the concrete is still ‘plastic’. Plastic Settlement Cracking is usually caused by an insufficient cover over the reinforcing. As the concrete cures, it pulls back slightly from the bars, causing cracking at the surface.

Settlement cracking diagram

2. PLASTIC SHRINKAGE CRACKING

— Shrinkage cracking is by far the most common cause of early surface cracking. It occurs when the upper layer of the concrete dries out faster than the lower layer. This, in turn, is caused by uneven hydration, and evaporation (moisture loss) exceeding bleed (moisture moving upwards through the fresh concrete). It is essential to maintain the concrete’s moisture levels in the critical 6 hours after pour – preferably for the first three days.
Shrinkage cracking diagram

EFFECT

So what’s the big deal? Why should those little cracks be a problem?
Small cracks provide channels for the entry of moisture-borne contaminants:

  • Oxygen
  • Carbon dioxide
  • Chlorides
  • … and more

Entrance of contaminants into concrete slabs via cracking

These contaminants are reactive, with either the concrete or the steel, and will set a cycle of deterioration in motion. As the concrete deteriorates, or the reinforcing steel corrodes, larger cracks will develop, and the cycle accelerates. The slab or structure faces a compromised service life and premature decay.

PREVENTION

Did you catch that little phrase, ‘moisture-borne’?
Contaminants are carried by moisture, including moisture vapour. Moisture helps drive many of the deleterious reactions inside the concrete. Moisture is an integral part of steel corrosion.
IMMOBILISE THE MOISTURE = ARREST OR PREVENT THE DETERIORATION!
This is where HYDROGEL technology shines.

  • FOR CURING – use spray-applied Aquron hydrogel treatment instead of a curing compound or water curing. This limits the evaporation and causes even hydration, resulting in high-quality curing.
  • FOR PROTECTION – Aquron hydrogel treatment can be incorporated as an admixture, or spray-applied, to protect new structures permanently from contaminant attack.
  • FOR LONG-TERM DURABILITY AND MAXIMUM SERVICE LIFE – Aquron hydrogel treatments will genuinely preserve concrete, making them extremely cost-effective. Think of it as a PRO-ACTIVE MAINTENANCE TOOL!

We’d love to talk to you in more detail about the requirements of your project!
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Aquron curing is equal or superior to water curing




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